Copper Fill of Microvia Using a Thiol-Modified Cu Seed Layer and Various Levelers

Abstract

Microvia filling by copper electroplating was carried out using a plating bath containing a suppressor and a leveler without an accelerator. The required accelerator was adsorbed onto the copper seed layer of the microvia in a predipping bath before the filling plating. This pretreatment is similar to the self-assembled monolayer of thiol molecules that forms on a copper surface. The suppressor was poly(ethylene glycol) (PEG), and five levelers, namely, Janus green B, diazine black, methylene violet, safranine O, and Alcian blue, were employed to screen for the best plating formula suitable for a plating process in which no accelerator was present in the plating solution. The thiol molecule employed in this work was 3-mercapto-1-propanesulfonate (MPS). The electrochemical behaviors of various plating formulas were characterized using a galvanostatic measurement on a copper electrode at different rotating speeds. Results indicated that the MPS adlayer is transferable onto the surface of the copper deposit and can be displaced by the PEG–Cl–leveler. The displacement rate depends on the molecular structure of the added leveler. This plating process has the potential to greatly reduce the plating time of microvia filling.